One of the most common practices for controlling undesirable plant species is the use of post-emergent selective herbicides. For example, certain compounds which inhibit the enzymes acetohydroxyacid synthase (AHAS), acetyl CoA carboxylase (ACC) and/or 5-hydroxyphenyl-pyruvate-dioxygenase (HPPD) are known herbicides which are effective against certain annual and perennial grass and broadleaf weeds. Unfortunately these herbicides cannot be used in all crops, especially cereal crops such as corn, wheat, barley and rice, because of unacceptable crop tolerance.
Therefore what is needed in the art is a herbicide which is effective against weeds, while protecting the gramineous crop from injury.
It is known, for example from U.S. Pat. No. 4,931,581 and U.S. Pat. No. 5,229,384, that certain benzothiadiazole derivatives have the capability to prevent healthy plants from attack by harmful microorganisms by stimulating the plants'own biological defense system. The term for the plant response on such stimulating agents is systemic acquired resistance (SAR).